System and Method for Removing a Cryporotectant from a Liquid

ABSTRACT

A system for removing cryoprotectant from a cryoprotectant-containing liquid stored a container comprises a cryoprotectant removal device that receives the cryoprotectant-containing liquid and a cryoprotectant-free dialysate liquid and that is operable to transfer cryoprotectant to the dialysate liquid. A differential conductivity device is arranged to continuously measure the difference in conductivity between dialysate liquid entering the device and dialysate liquid that has received cryoprotectant transferred by the dialyzer discharged from the device. A controller is operable to control the flow of the liquids through the device in response to the measured difference in conductivity, and particularly to stop the flow of the cryoprotectant-containing liquid when the measured differential conductivity indicates that the cryoprotectant has been substantially removed from the liquid.

REFERENCE TO RELATED APPLICATION

The present application claims priority to co-pending provisionalapplication No. 61/079,282, filed on Jul. 9, 2008, in the name of thepresent inventor, and entitled “System for Detecting the Presence of aSubstance in a Fluid.” The disclosure of this application No. 61/079,282is incorporated herein by reference.

BACKGROUND

The present disclosure concerns systems and methods for detecting thepresence of substances in a liquid, such as blood and other bodilyliquids. One application of the system and method disclosed herein is todetect the presence of preservation substances, such as DMSO, in acryogenically-treated blood sample that is being treated to remove theDMSO.

It is known to utilize various cryoprotectants, such as dimethylsulfoxide (DMSO), during cryopreservation cells. Use of a cryoprotectantis essential to prevent cryoinjury to the cells, such as from theformation of intracellular ice crystals during freezing. Thus, in stemcell transplant treatments, for instance, the stem cells are obtainedand frozen, to be later thawed for periodic treatments of a patientaffected by cancer or other diseases. In some prior treatments, thefrozen-thawed stem cells are injected into the patient, along with thecryoprotectant, because there have been no effective ways to remove thecryoprotectant without losing a significant amount of stems cells orotherwise contaminating them. However, at room or body temperature,certain cryoprotectants, such as DMSO, are known to be toxic to cells aswell as the patient. For instance, DMSO is known to cause ill effects inpatients, ranging from fever and nausea to violent cramping. In somecases, the presences of cryoprotectant may endanger the patient's life.The potentially dangerous effects of cryoprotectants on the patient hastempered the desirability of using frozen and banked cells or liquids ofany type.

One common method for removal of cryoprotectant has been mechanicalremoval, typically in the form of centrifugation followed byresuspension in a media to remove the cryoprotectant by dilution.However, the mechanical forces introduces during centrifugation resultin osmotic stress and cell clumping/lysing, particular for fragilecells. Moreover, the generally open nature of centrifugation may resultin bacterial or viral contamination of the cell preparation.

In order to address these problems a closed system has been developed asdisclosed in U.S. Pat. No. 6,869,758 (the '758 patent), assigned to theUniversity of Kentucky Research Foundation. The disclosure of the '758patent is incorporated herein by reference. The '758 patent disclosespassing the cryoprotectant-containing liquid through at least onesemipermeable hollow fiber membrane contained in a hollow module in afirst direction to contact the hollow fiber membrane on at least oneinterior surface. Concurrently, a liquid which is substantially free ofcryoprotectant is passed through the hollow module in a second direction(opposite the first direction) so that the cryoprotectant-free liquidcontacts the semipermeable hollow fiber membrane on at least oneexterior surface. A diffusion gradient is thus created that transfersthe cryoprotectant from the cryoprotectant-containing liquid to thecryoprotectant-free liquid for subsequent removal.

Thus, in the treatment of a frozen-thawed cell suspension containing acryoprotectant, the hollow module and semipermeable hollow fibermembrane disclosed in the '758 patent can be connected directly to thesource of the suspension. In the case of frozen-thawed blood, the devicedisclosed in the '758 patent can be connected to the blood bag in aclosed system. The system may incorporate a series of pumps and valvesto move the cell suspension liquid and the cryoprotectant-free liquidthrough the system. Details of one such system are shown in FIG. 2 anddescribed herein.

The system disclosed in the '758 patent provides a completely closedsystem for the effective removal of cryoprotectant from a liquid. Sincethe system relies upon diffusion and the dialysis process, there is nodamage to the desired cells if the process is optimally performed.Moreover, the process retains a significant quantity of the originalfrozen-thawed liquid, again if optimally performed. In order to achieveoptimal performance, it is desirable that the cryoprotectant removalprocess continue only for as long as necessary to reduce the presence ofcryoprotectant in the cell suspension to a suitable level. While theclosed system is less harmful to the desired cells than the priormechanical methods, “over-treatment” of the cells can cause damage andreduce the quantity of viable cells. On the other hand, “undertreatment” does not remove enough of the cryoprotectant, so that thedamaging effects of the cryoprotectant remain. Thus, there is a need fora system and method for determining when the dialysis process iscomplete.

SUMMARY

According to one aspect of the invention, a system is provided forremoving cryoprotectant from a cryoprotectant-containing liquid stored acontainer that comprises a cryoprotectant removal device that receivesthe cryoprotectant-containing liquid and a cryoprotectant-free dialysateliquid and that is operable to transfer cryoprotectant to the dialysateliquid. A differential conductivity device is arranged to continuouslymeasure the difference in conductivity between dialysate liquid enteringthe device and dialysate liquid that has received cryoprotectanttransferred by the dialyzer discharged from the device. A controller isoperable to control the flow of the liquids through the device inresponse to the measured difference in conductivity, and particularly tostop the flow of the cryoprotectant-containing liquid when the measureddifferential conductivity indicates that the cryoprotectant has beensubstantially removed from the liquid.

In a further aspect, the cryoprotectant removing device is a dialyzerhaving a first inlet to receive the cryoprotectant-containing liquid, afirst outlet for discharge of the cryoprotectant-liquid, a second inletto receive a cryoprotectant-free dialysate liquid and a second outletfor discharge of the cryoprotectant-free liquid, the dialyzer forming adiffusion gradient between the cryoprotectant-containing liquid and thecryoprotectant-free liquid. The system further comprises an outlet fluidline connected to the first inlet and connectable to an outlet of thecontainer, and an inlet fluid line connected to the first outlet andconnectable to an inlet of the container, the outlet and inlet fluidlines forming a first fluid circuit between the container of thecryoprotectant-containing liquid and the dialyzer. A second outlet fluidline is connected between the source of dialysate liquid and the secondinlet, and a discharge fluid line is connected to the second outlet andconnectable to a waste container, the second outlet fluid line and thedischarge fluid line forming a second fluid circuit between the sourceof dialysate liquid and the dialyzer.

A first pump is disposed in the first fluid circuit for controlling theflow of the cryoprotectant-containing liquid through the first fluidcircuit, and a second pump is disposed in the second fluid circuit forcontrolling the flow of the dialysate liquid through the second fluidcircuit. In one feature, the differential conductivity device isdisposed between the second outlet fluid line and the discharge fluidline and is operable to measure the difference in conductivity betweendialysate liquid flowing through the second outlet fluid line anddialysate liquid that has received cryoprotectant transferred by thedialyzer flowing through the discharge fluid line. The controller isconfigured to control the operation of the first and/or second pump inresponse to the measured difference in conductivity.

A method is provided for removing cryoprotectant from a liquid whichcomprising the step of passing a cryoprotectant-containing liquid and acryoprotectant-free liquid through a cryoprotectant removal deviceconfigured to transfer cryoprotectant from the cryoprotectant-containingliquid to the cryoprotectant-free liquid. In one feature, the methodincludes measuring the differential conductivity betweencryoprotectant-free liquid entering the device and cryoprotectant-freeliquid discharged from the device after receiving cryoprotectanttransferred within the device. The method further contemplatescontrolling the flow of the cryoprotectant-containing liquid and/or thecryoprotectant-free liquid through the device in response to themeasured differential conductivity.

DESCRIPTION OF THE FIGURES

FIG. 1 is a side view of a conductivity cell for use with a closedsystem for removing cryoprotectant from a liquid.

FIG. 2 is a diagram of a closed system for removing cryoprotectant froma liquid, incorporating the conductivity cell shown in FIG. 1, with thesystem in a first state for priming the system.

FIG. 3 is a diagram of the closed system shown in FIG. 2, with thesystem in a second state for commencing blood flow from a blood bagthrough the system.

FIG. 4 is a diagram of the closed system shown in FIG. 2, with thesystem in a third state for directing blood flow back to the blood bag.

FIG. 5 is a diagram of the closed system shown in FIG. 2, with thesystem in a subsequent state for directing flow of dialysate through thesystem.

FIG. 6 is a diagram of the closed system shown in FIG. 2, with thesystem in a fifth state for recovering blood cells remaining in thesystem after the prior steps.

FIG. 7 is a diagram of the closed system shown in FIG. 2, with thesystem in a further state for recovering additional blood cellsremaining in the system after the prior steps.

DESCRIPTION OF THE EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and described in the following written specification. It isunderstood that no limitation to the scope of the invention is therebyintended. It is further understood that the present invention includesany alterations and modifications to the illustrated embodiments andincludes further applications of the principles of the invention aswould normally occur to one skilled in the art to which this inventionpertains.

Conductivity Cells

The present invention contemplates the integration of conductivitycells, such as the cells 22, 24 depicted in FIG. 1, within closed system10 shown in FIG. 2 for removal of cryoprotectant from a liquid, such asblood or a cell suspension. As shown in FIG. 1, the conductivity cells22, 24 include flow-through conductivity electrodes 26 and 28 that arecoupled to tubing 30, 32. The tubing from part of the closed system 10,as explained herein. The electrodes are separated by tubing 34 by apredetermined distance to achieve a desired conductivity cell constantK. In one specific embodiment, the electrodes are stainless steeltubing, having a length of about 4.0 cm, an outer diameter of about 0.48cm. and an inner diameter of about 0.38 cm. The tubing 34 is sized toseparate the electrodes by about 9.0 cm to achieve a cell constant offifty. The high cell constant helps minimize the effects of conductivitycell fouling. In the specific example, the conductivity cells areconfigured to detect the presence of DMSO in blood. Other cell constantsmay be preferable for detecting other cryoprotectants in other liquids.

The electrodes are connected to a conductivity meter in a conventionalmanner, such as with alligator clips. Alternatively, the electrodes mayincorporate contact points or wiring configured to connect to aconductivity meter. One suitable conductivity meter is the YSI® Model 32meter. In addition, the electrodes 26, 28 may incorporate fluid fittingsto facilitate connection to the existing tubing 30, 32 of the closedsystem 10. For instance, the ends of the electrodes 26, 28 mayincorporate a barbed fitting.

Closed System for Removing Cryoprotectant from aCryoprotectant-Containing Liquid

The closed system 10 for removing cryoprotectant from a liquid may beconstructed as shown in FIG. 2 to incorporate the dialyzer 12 disclosedin the '758 patent discussed above. Although the specifics of thedialyzer 12 are found in the '758 patent, the disclosure of which isincorporated herein by reference, certain parts of the structure areshown in the present figure. In particular, the dialyzer 12 includes afirst inlet 13 and a first outlet 14, as well as a second inlet 16 and acorresponding second outlet 17. The first inlet 13 is connected to thesource of the cryoprotectant-containing liquid, while the second inlet16 is connected to a source of cryoprotectant-free liquid. Thecorresponding outlets 14 and 17 discharge the liquids exiting thedialyzer 12.

The closed system 10 shown in FIG. 2 provides a closed fluid circuitcommencing with fluid couplings C adapted to be coupled to a liquidsource, such as a blood bag B as shown in FIG. 3. One coupling isconnected to an outlet fluid line 50 through a valve V2, which in turnis connected to the first inlet 13 of the dialyzer 12 through a pump P1.The other coupling C is connected to a return fluid line 52 which inturn is connected to the first outlet 14 of the dialyzer 12 through avalve V3. A conductivity cell 40 may be interposed between the returnfluid line 52 and the first outlet 13 of the dialyzer. As thus fardescribed, the system 10 provides a closed fluid circuit that passes acryoprotectant-containing liquid through the dialyzer which returnsliquid to the source that has had the cryoprotectant level reduced bythe dialyzer 12.

The operation of the dialyzer 12 depends upon the passage of acryoprotectant-free liquid counter-flow to the flow ofcryoprotectant-containing liquid through the dialyzer. Thus, the closedsystem 10 further includes a source S of a cryoprotectant-free liquid,or dialysate, such as an isotonic salt solution. This source S isconnected to the second inlet 16 of the dialyzer 12 by a dialysate line54 through a valve V1. The dialysate is discharged from the dialyzer 12at second outlet 17 connected to dialysate discharge line 56. Since thedialysate discharged from the dialyzer includes a quantity ofcryoprotectant removed from the other liquid passing through the device,the discharged dialysate is sent to a waste container W. A pump P2 isincorporated into the dialysate circuit to draw the dialysate throughthe dialyzer 12. The pumps P1 and P2 are sized to achieve an appropriateflow rate of the cryoprotectant-containing liquid and the dialysate foroptimum performance of the dialyzer. In a specific example, the twopumps of the system 10 are adjustable flow pumps capable of operating ata maximum flow rate of 150 ml/min.

A priming circuit is also provided to prime the dialyzer 12. The circuitincludes a source PS of priming solution with two output lines 60 and62. The output line 60 is connected through a valve V5 to the dialysateline 54. The output line 62 is connected through a valve V6 to the firstinlet 13 of the dialyzer 12, or more particularly to the outlet line 50through which the cryoprotectant-containing liquid is provided. Thepriming solution flows through the dialyzer 12 prior to its operation onthe cryoprotectant-containing liquid.

In accordance with one aspect of the invention, a differentialconductivity device 20 is introduced into the dialysate circuit. Inparticular the device 20 includes a conductivity cell 22 connectedacross the outlet line 54 from the dialysate source S, and aconductivity cell 24 connected across the discharge line 56 prior to thepump P2 and waste container W. The differential conductivity device 20generates differential conductivity readings for the dialysate enteringand exiting the dialyzer 12 during operation. A third conductivity cell40 is provided at the outlet 14 of the dialyzer 14 to measure theconductivity of the cryoprotectant-containing liquid after it has beentreated in the dialyzer.

It is known that the readings produced by the conductivity cells 22, 24and 40 will vary with temperature. In order to obtain accuratemeasurements the readings are temperature compensated. Thus, atemperature probe is positioned close to each conductivity cell. Inparticular, as shown in FIG. 2, a temperature sensor T1 is adjacent cell22, sensor T2 is adjacent cell 24 and temperature sensor T3 adjacentcell 40. An additional temperature sensor T4 may be provided at theblood inlet to the dialyzer 12.

Operation of the Closed System

Start-Up/Priming

At start-up, the system shown in FIG. 2 pumps a priming solution intoboth parts of the dialyzer. The presence of the priming solution in thevarious lines of the fluid circuits is indicated by the notation“Priming”. In one embodiment, the priming solution is distilled water.Valve V6 is open to direct priming solution from container PS into theinlet 13 of the dialyzer, while valve V5 is open to direct primingsolution into the dialysate inlet 16. Valves V1 and V2 connected to thedialysate source S and couplings C are both closed during priming of thedialyzer 12. The priming solution is pumped through the dialyzer bypumps P1 and P2, preferably at 150 ml/m. As shown in FIG. 2, the primingsolution fed into the dialysate inlet 16 first passes throughconductivity cell 22, while conductivity cell 24 receives the solutionexiting at the dialysate outlet 17. The priming solution exiting thedialyzer at the first outlet 14 is directed by closed valve V3 and openvalve V4 to the waste container W for appropriate disposal. Likewise,solution exiting through second outlet 17 is pumped into the wastecontainer.

As the priming solution flows through the system as shown in FIG. 2,measurements at the conductivity cells 22, 24 and 40 are temperaturecorrected. Correction factors are determined for cells 24 and 40 thatadjust the measurements at these cells to be equal to the measurementvalue of conductivity cell 24, since the same liquid, the primingsolution, is flowing through each cell In a preferred embodiment, thetemperature and conductivity values are maintained within predeterminedrange and are permitted to vary within predetermined narrow boundaryvalues. Quick spikes in the readings could be an indication of bubblesin the system. After five minutes priming the dialyzer, the readings ofthe conductivity cells should become stable.

Detecting Blood Cells

Once the dialyzer 12 has been primed, a blood bag B is connected to theliquid couplings C, as shown in FIG. 3. In one embodiment, the bloodcontains a cryoprotectant used in a cryogenic process to store the bloodsample. The cryoprotectant may be DMSO and may be in solution in theblood in varying percentages. A suitable dialysate to remove the DMSO isa phosphate buffered saline (PBS). The dialyzer 12 is configured asdisclosed in the '758 patent to remove the DMSO, returning substantiallypure blood to the blood bag for subsequent use.

The state of the fluid circuit for blood detection within the system 10is illustrated in FIG. 3. When the blood bag is attached, valve V2 isopened so blood solution is pumped into the blood inlet 13 of thedialyzer by pump P1, as indicated by the designation “Blood” in thesystem 10. The blood is preferably pumped at 30 psi. When the bloodfirst starts to flow into the dialyzer, valve V3 is closed and valve V4is opened to purge any residual priming solution from the dialyzer bloodcircuit through outlet 14 to the waste container W. The blood flowingthrough the system has a higher concentration of DMSO than the primingsolution PBS. Thus, conductivity cell 40 will show the first indicationof the higher resistance of blood solution versus the priming solutionthat had passed through the cell in the previous priming step shown inFIG. 2.

The priming solution PBS is pumped through the dialysate fluid circuitby the pump P2, since the valve V5 is open and the valve V1 to thedialysate source S is closed. The resistance measured by theconductivity cell 24 will also increase as the blood starts through thesystem because blood will cross the dialyzer into the priming solutionpresent in the dialysate circuit formed by fluid lines 54 and 56.Nominally, conductivity cell 40 will indicate a higher resistance thanconductivity cell 24 because the DMSO-containing blood transferredthrough the dialysis membrane of the dialyzer will necessarily becomediluted by the priming solution already within the dialysate loop.

Blood Flow Back to Blood Bag

A change in measurement reading at conductivity cell 40 indicates whenthe blood has arrived at the cell, meaning that the blood has passedthrough the dialyzer 12. At this point, the blood flow is redirectedback to the blood bag by closing valves V4 and opening valve V3, asshown in FIG. 4. It should be noted that as in the prior blood detectionstep, the priming solution continues to be pumped through the dialysatecircuit and into the waste container at 150 psi. The priming solution isnot adapted to extract the DMSO from the blood.

As the blood continues to flow through the dialyzer, the difference ofthe conductivity measurements between conductivity cells 22 and 24 willapproach a predetermined value that is near zero. A near-zerodifferential conductivity means that the dialysate circuit is fullyprimed and ready to receive the dialysate from the source S.

When the differential conductivity between cells 22 and 24 reaches thepredetermined value, valve V5 is closed to terminate flow of primingsolution through the system, as shown in FIG. 5. (Valve V6 may also beclosed). Valve V1 is then opened to direct the dialysate PBS through thedialysate circuit of fluid lines 54 and 56, as indicated by thedesignation “Isotonic”. When the isotonic solution is flowed through thedistillate side of the dialyzer 12 the differential conductivitymeasurements will follow the same pattern as for the priming solution.Thus, the difference in measurements at conductivity cells 22 and 24will show the removal of the DMSO and the conductivity values registeredby conductivity cell 40 at the blood outlet 14 will reflect the changesto DMSO concentration in the blood solution.

By continuing the flow of blood solution and isotonic solution throughthe dialyzer as shown in the FIG. 5, the viable cells in the bloodsolution can be concentrated. The integral of the area under thetemperature compensated conductivity curve for conductivity cell 40should indicate the concentration of DMSO-free blood cells beingreturned to the blood bag. It is contemplated that the measurement ofthe conductivity cell 40 will reach a predetermined value indicative ofremoval of all or substantially all of the DMSO from the blood solution.

Shut Down

The conductivity cells can be used to detect the process of pushingviable cells from the dialyzer into the blood bag. In the system 10 isconfigured to push substantially all of the available viable cells intothe blood bag using the priming solution. As shown in FIG. 6, valve V2is closed to terminate blood flow to inlet 13, since the blood solutionhas been substantially purified. Valve V6 is then opened so that primingsolution will flow into the inlet 13 behind the blood cells within thedialyzer 12. The isotonic solution continues to flow through thedistallate circuit 54, 56 and to the waste container W. This progress ofthe process is indicated by conductivity changes in cells 24 and 40 todetermine when valve V3 should be closed. In other words, when theconductivity measurements of conductivity cell 40 changes from theconductivity value for purified blood to the conductivity value forpriming solution, it can be determined that all of the blood cells havebeen pushed out of the dialyzer. A similar change will be reflected atconductivity cell 24, although of a lesser magnitude, as bloodcross-over into the dialysate circuit ceases.

Flow Reversal

In a final step, the flow of pump P1 is reversed to pushing any bloodcells remaining in the outlet line 50 back into the blood bag B. Thus,as shown in FIG. 7, valve V2 is opened, pump P1 is reversed, and valveV4 is opened to permit flow through the pump behind the blood cells.Flow of the isotonic solution through the dialyzer is ceased by stoppingpump P2, while valves V5 and V6 are closed to terminate any primingsolution flow. Thus, there will be no indication of activity at theconductivity cells 22 and 24. However, conductivity cell 40 will measurethe conductivity changes from isotonic solution to priming solution,which may be used to indicate a stopping point for the process.Alternatively, the duration of the process may be limited to apredetermined time believed to be sufficient to return all viable bloodcells to the blood container. This can be achieved in one embodiment bycounting steps of the stepper motor driving pump P1, or by a direct timemeasurement to indicate when to de-energize the pump.

In certain cases, some of the blood returning to the blood bag throughfluid line 52 can be immediately drawn back through the system throughoutlet line 50. This phenomenon can lead to a false indication of areduction in DMSO in the blood. This occurrence can be prevented bysegmenting the blood bag B that will prevent the returning “clean” bloodfrom displacing the untreated blood remaining in the bag. In oneapproach, a baffle is created between the ports on the blood bag toprevent any cross-contamination. Other approaches may be implemented toensure that all of the untreated blood in the blood bag B flows throughthe closed system 10 before the conductivity cells indicate a DMSO levelindicative that the DMSO has been substantially removed from the blood.

It is contemplated that the sequence of opening and closing the valvesV1-V6 and activating/de-activating pumps P1 and P2 can be controlled bya master controller. The controller receives signals from theconductivity cells 22, 24 and 40, as well as from the temperaturesensors T1-T3, and generates control signals for the opening and closingthe valves and for energizing, de-energizing and controlling flow rateand direction of the pumps P1 and P2. The controller may be analog withappropriate circuitry to evaluate measurement differences between cellsand between cell measurements and threshold values.

Preferably, the components are digital and the controller is aprogrammable microcontroller. The digital controller can adjust theconductivity measurements generated by each conductivity cell inrelation to the temperature measured by the adjacent temperature sensor.Adjusted values for the conductivity cells 22 and 24 can be used togenerate the differential conductivity values used to determine when thecryoprotectant has been substantially removed from the blood. Theadjusted values of all the cells can also be compared as described aboveto determine when the priming step has completed or when substantiallyall of the blood cells have been returned to the blood bag B.

The controller can also be configured to compare the differential andactual conductivity values to the various thresholds used to determinewhen one step is complete and another is to begin. The controller maypermit user input to change the threshold values based on a particularcryoprotectant, cryoprotectant-containing liquid, dialysate or primingsolution. Alternatively, or additionally, the controller may incorporatea data base of stored values that can be selected by identifying theparticular combination of liquids. In addition to storing thresholdvalues, the controller may also store the desired pump flow rates forthe various steps of operation of the system 10.

It is further contemplated that the controller may be configured tomonitor the rate of change in conductivity or differential conductivityat the differential conductivity device 20 as an indication of the rateor removal of cryoprotectant from the blood. In some circumstances,removal that occurs to rapidly can damage the blood cells. Thus, whenthe rate of change of conductivity or differential conductivity exceedsa predetermined threshold value the controller can alter the flowthrough the system 10, such as by reducing the flow rate of one or bothof the pumps P1 and P2, to thereby protect the blood cells from rapidosmolality change.

Conductivity tests using the conductivity cell disclosed herein havebeen conducted to establish baseline values for certain substances andto evaluate the change in these values with temperature. For instance,tests for distilled water show a conductivity of 1.10 E-07 mohs at 10°C. and an essentially linear 2.43% change in conductivity per eachdegree of temperature change. Similar tests on a 10% DMSO solution showinitial conductivity of 5.34 E-02 mohs and a rate of change of 2.10%.The conductivity at 10° C. increases to 6.48 E-02 mohs for a 2.5% DMSOsolution while the rate of change with temperature decreases to 1.97%.Similar tests for a 4.5% PBS solution show a conductivity at 10° C. of3.93 E-04 mohs and a rate of change of 1.76%, with the conductivitydecreasing to 7.20 E-05 mohs and rate of change increasing to 1.84% fora 0.9% PBS solution. The conductivity values for sucrose are 3.50 E-07mohs and 2.40%.

These test results reveal a difference in magnitude of conductivityvalues among the various substances flowing through the closed system 10and the differential conductivity device 20. Thus, the differentialconductivity readings used to determine when the blood is substantiallyfree of cryoprotectant will be very pronounced initially since the lowerconductivity pure dialysate PBS will be flowing through the cell 22 andthe much higher conductivity PBS-DMSO solution exiting the dialyzer 12will be flowing through the second cell 24. The amount of DMSO purgedfrom the blood flowing through the dialyzer 12 decreases with each passof the blood through the system so that the conductivity of the liquidflowing through the second cell 24 will gradually decrease to match theconductivity of the pure dialysate PBS at cell 22.

The closed system 10, the differential conductivity device 20 and theconductivity cell 40, as well as the protocol disclosed herein, can beused very effectively to remove cryoprotectant from a quantity of bloodthat has been previously frozen and then thawed. The same system andprotocol can be used to remove other cryoprotectants from blood, such asglycerol, provided the conductivity values are different enough from thebaseline liquids and/or that the conductivity cells are sensitive enoughto measure more subtle differences in conductivity. Moreover, thepresent system 10 and the protocol described above can be used tomonitor the removal of other substances from a particular liquid, againprovided the conductivity values and change in conductivity are readilydetectable by the conductivity cells.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same should be considered asillustrative and not restrictive in character. It is understood thatonly the preferred embodiments have been presented and that all changes,modifications and further applications that come within the spirit ofthe invention are desired to be protected.

1. A system for removing cryoprotectant from a cryoprotectant-containing liquid stored a container comprising: a dialyzer having a first inlet to receive the cryoprotectant-containing liquid, a first outlet for discharge of the cryoprotectant-liquid, a second inlet to receive a cryoprotectant-free dialysate liquid and a second outlet for discharge of the cryoprotectant-free liquid, said dialyzer forming a diffusion gradient between said cryoprotectant-containing liquid and the cryoprotectant-free liquid; a source of cryoprotectant-free dialysate liquid capable of receiving cryoprotectant transferred through said diffusion gradient within said dialyzer; an outlet fluid line connected to said first inlet and connectable to an outlet of the container; an inlet fluid line connected to said first outlet and connectable to an inlet of the container, said outlet and inlet fluid lines forming a first fluid circuit between the container of the cryoprotectant-containing liquid and said dialyzer; a second outlet fluid line connected between said source of dialysate liquid and said second inlet; a discharge fluid line connected to said second outlet and connectable to a waste container, said second outlet fluid line and said discharge fluid line forming a second fluid circuit between said source of dialysate liquid and said dialyzer; a first pump disposed in said first fluid circuit for controlling the flow of the cryoprotectant-containing liquid through said first fluid circuit; a second pump disposed in said second fluid circuit for controlling the flow of the dialysate liquid through said second fluid circuit; a differential conductivity device disposed between said second outlet fluid line and said discharge fluid line and operable to measure the difference in conductivity between dialysate liquid flowing through said second outlet fluid line and dialysate liquid that has received cryoprotectant transferred by said dialyzer flowing through said discharge fluid line; and a controller for controlling the operation of said first and/or second pump in response to the measured difference in conductivity.
 2. The system for removing cryoprotectant according to claim 1, further comprising: a first valve disposed in said first outlet fluid line, said first valve openable to permit and closable to prevent flow of cryoprotectant-containing liquid from the container to said dialyzer; and a second valve disposed in said second outlet fluid line, said second valve openable to permit and closable to prevent flow of dialysate liquid from said source to said dialyzer, wherein said controller is configured to open or close said first and/or second valve in response to the measured difference in conductivity.
 3. The system for removing cryoprotectant according to claim 1, further comprising: a first temperature sensor adjacent said differential conductivity device and arranged to measure the temperature of liquid flowing through said second outlet fluid line; and a second temperature sensor adjacent said differential conductivity device and arranged to measure the temperature of liquid flowing through said discharge fluid line, wherein said controller is further configured to adjust the measured difference in conductivity as a function of the temperature sensed by said first and second temperature sensors.
 4. The system for removing cryoprotectant according to claim 1, further comprising: a source of a priming solution for preparing said dialyzer; a first priming outlet fluid line connected between said source of priming solution and said first inlet of said dialyzer; and a second priming outlet fluid line connected between said source of priming solution and said second inlet of said dialyzer.
 5. The system for removing cryoprotectant according to claim 4, wherein: said first priming outlet fluid line intersects said first fluid circuit so that said first pump is operable to flow said priming solution through said dialyzer; and said second priming outlet fluid line intersects said second fluid circuit so that said second pump is operable to flow said priming solution through said dialyzer and so that said priming solution flows through said differential conductivity device.
 6. The system for removing cryoprotectant according to claim 5, further comprising: a third valve disposed in said first priming outlet fluid line, said third valve openable to permit and closable to prevent flow of priming solution from said source of priming solution to said dialyzer; and a fourth valve disposed in said second priming outlet fluid line, said fourth valve openable to permit and closable to prevent flow of priming solution from said source of priming solution to said dialyzer, wherein said controller is configured to open or close said third and/or fourth valve in response to the measured difference in conductivity.
 7. The system for removing cryoprotectant according to claim 1, further comprising: a conductivity cell disposed in said inlet fluid line adjacent said dialyzer, said conductivity cell arranged to measure the conductivity of liquid flowing through said inlet fluid line; a waste fluid line intersecting said inlet fluid line between said conductivity cell and the inlet to the container of the cryoprotectant-containing liquid, said waste fluid line connectable to a waste container; and a fifth valve disposed in said waste fluid line between said inlet fluid line and the waste container, said fifth valve openable to permit and closable to prevent flow of liquid from said dialyzer to the waste container, wherein said controller is configured to open or close said fifth valve in response to the measured conductivity.
 8. The system for removing cryoprotectant according to claim 7, further comprising: a third temperature sensor adjacent said conductivity cell and arranged to measure the temperature of liquid flowing through said inlet fluid line, wherein said controller is further configured to adjust the measured conductivity as a function of the temperature sensed by said third temperature sensor.
 9. A method for removing cryoprotectant from a liquid comprising the steps of: passing a cryoprotectant-containing liquid and a cryoprotectant-free liquid through a cryoprotectant removal device configured to transfer cryoprotectant from the cryoprotectant-containing liquid to the cryoprotectant-free liquid; measuring the differential conductivity between cryoprotectant-free liquid entering the device and cryoprotectant-free liquid discharged from the device after receiving cryoprotectant transferred within the device; and controlling the flow of the cryoprotectant-containing liquid and/or the cryoprotectant-free liquid through the device in response to the measured differential conductivity.
 10. The method for removing cryoprotectant of claim 9, wherein the step of controlling the flow comprises continuously comparing the measured differential conductivity value to a predetermined threshold value indicative that the liquid discharged from the device is substantially free cryoprotectant.
 12. The method for removing cryoprotectant of claim 9, further comprising the steps of: passing a priming solution through the device prior to operating the device to remove cryoprotectant; upon completion of the priming step, flowing cryoprotectant-containing liquid through the device; continuously measuring the conductivity of liquid discharged from the device; and diverting the liquid discharged from the device to a waste container until the measured conductivity reaches a predetermined threshold value indicative that only cryoprotectant-containing liquid is flowing through the device.
 13. The method for removing cryoprotectant of claim 9, wherein the measuring step includes measuring the temperature of the cryoprotectant-free liquid entering the device and liquid discharged from the device and adjusting the differential conductivity as a function of the measured temperatures. 